1. Field of the Invention
The present invention relates to an apparatus for optically correcting image blur occurring in photographing on vehicles or caused by a camera shake.
2. Related Background Art
Conventionally, various photographing lenses have been proposed, which have a blur correcting means for moving a correcting lens unit as a part of a photographing lens in a direction perpendicular to the optical axis to correct blur of a photographed image occurring when vibrations are transmitted to a photographing system.
As an example, Japanese Laid-Open Patent Application No. 62-44707 has proposed a photographing lens having a blur correcting means for correcting blur of a photographed image occurring when photographing is performed on moving objects, such as running vehicles or flying airplanes, by moving a correcting lens unit in a direction perpendicular to the optical axis.
FIGS. 9A, 9B, and 10 are schematic views each showing an optical system in which light beams passing through individual lens units are illustrated assuming that a partial lens unit 12 constituting a zoom lens is used as a correcting lens unit and this lens unit 12 is moved in a direction perpendicular to the optical axis to correct blur of a photographed image.
Referring to FIGS. 9A and 9B, a magnification change from a wide-angle end to a telephoto end is performed by moving the lens unit 12 in the direction of optical axis toward an image surface as indicated by an arrow, and a variation in an image surface caused by the magnification change is corrected by moving a lens unit 11 nonlinearly in the optical axis direction. This optical system also includes a diaphragm 15 with a variable aperture diameter and a relay lens unit 13 kept fixed during the magnification change.
FIGS. 9A and 9B illustrate conditions in which light beams propagate through the individual lens units in a zoom position at the wide-angle end and in a zoom position at the telephoto end, respectively. FIG. 10 illustrates a condition in which light beams propagate through the individual lens units in the zoom position shown in FIG. 9B when the lens unit 12 is moved upward in the drawing surface in a direction (to be also referred to as a "positive direction" hereinafter) perpendicular to the optical axis to correct blur of a photographed image.
Generally, to correct blur of a photographed image, a partial lens unit constituting a photographing lens, e.g., a lens unit before a diaphragm is used as a correcting lens unit. When this correcting lens unit is decentered parallel in the positive direction (upward), a quantity of light increases in a negative portion ha where an image height extends downward and largely decreases in a positive portion hb where the image height extends upward. This produces a significant difference in illuminance of the field between the upper and lower portions of a screen, resulting in a variation in brightness on the screen.
When a lens unit (e.g., the lens unit 13) behind the diaphragm is used as the correcting lens unit, the relationship of a difference in light quantity between the peripheral portions of the screen is reversed. This significantly degrades the quality of a photographed image.
Another example is shown in FIG. 11 in which it is assumed that a blur correcting optical system consisting of a convex lens unit 103 is arranged behind an afocal optical system consisting of a convex lens unit 101 and a concave lens unit 102. This correcting optical system 103 is held by a lens frame 104 as optical axis decentering means. The lens frame 104 is so supported as to be movable two-dimensionally in a plane perpendicular to the optical axis with respect to a fixed frame 105. An image on an image formation surface 106 is moved by the movement of the correcting optical system 103.
An angular deviation meter 107 for detecting a camera shake outputs an angular shake occurring in a camera, i.e., an angular deviation signal .theta.. This angular deviation signal .theta. is converted into an image blur correcting deviation signal d by a coefficient converter 108, and this image blur correcting deviation signal d is supplied to an actuator 109 via an operational amplifier 111. In accordance with the image blur correcting deviation signal d supplied, the actuator 109 operates to shift the lens frame 104.
A position sensor 110 constituting position detecting means for detecting an actual positional deviation of the lens frame 104 constitutes a feedback loop in which a signal d.sub.L from the position sensor 110 is fed back to the input system of the actuator 109 via the operational amplifier 111 to cause driving control of the lens frame 104 and the correcting optical system 103 to correspond to a vibration deviation.
With the above arrangement, since the lens frame 104 is so driven as to cancel image blur due to a camera shake, image blur correction can be performed.
Note that a camera shake causing image blur consists of two components, an up-and-down component (a component in the pitch direction) and a right-and-left component (a component in the yaw direction). Therefore, two sets of the angular deviation meters 107 and the operational amplifiers 111 are prepared to correct both the pitch shake and the yaw shake of a camera.
In the above conventional example, however, the correcting optical system 103 is movable within a predetermined range, e.g., .+-.d.sub.0 with respect to the optical axis, so a space of at least d.sub.0 must be provided between the lens frame 104 and the fixed frame 105. Therefore, an unnecessary light ray L not contributing to image formation may reach the image formation surface 106 through the space d.sub.0.
Note that in the case of a single lens with a fixed focal length as in the above conventional example, it is relatively easy to form a lens arrangement which does not allow incidence of the unnecessary light ray L onto the image formation surface 106. In the case of a zoom lens, however, there is a high possibility that the unnecessary light ray reaches the image formation surface 106.
FIG. 12 shows a zoom-type image blur correcting optical system in which in a zooming operation from Wide to Tele, first to third lens units are moved as illustrated, whereas a fourth lens unit and a diaphragm 112 are kept fixed. An image on an image formation surface 106 is moved by shifting the second lens unit, thereby correcting image blur.
Note that since the second lens unit is moved in the direction of optical axis in the zooming operation, mechanical members, such as a lens frame 104, a fixed frame 105, and an actuator, are also moved together in the optical axis direction.
In this arrangement, an unnecessary light ray passing between the lens frame 104 and the fixed frame 105 is L.sub.W at the Wide end and L.sub.T at the Tele end. The light ray L.sub.W reaches a position outside the image formation surface 106, and the light ray L.sub.T is interrupted by a frame (not shown) for holding the third lens unit; neither of the light rays reach the image formation surface 106.
Note that FIG. 12 demonstrates unnecessary light rays at the time the correcting optical system 103 is located at the origin. Therefore, even if no unnecessary light ray reaches the image formation surface in this condition, when the correcting optical system 103 is shifted in image blur correction, a space on the side opposite to the direction of shift is increased, and this allows the unnecessary light ray L.sub.W or L.sub.T to reach the image formation surface to produce a ghost.
The unnecessary light ray L.sub.W or L.sub.T introduces another problem that it penetrates as stray light into the image blur correcting optical mechanism and is incident on a light-receiving element (to be described later) as a position detecting means of the correcting optical system. This causes an error in an output from the light-receiving element, and the result is a reduction in image blur correction accuracy. One related art is disclosed in U.S. Pat. No. 4,907,868.